Magnetic recording by means of a thermal transducer



June 1, 1965 L.. E. FAY 1n @15833355 MmNEmIt RECORDING BY MEANS oFy A@ THERMA'UJ mwsnucmv Filed Dec. 2OI 19.61

I @fammes i p5-NER- Jawcmw' gemas i mf /fvfo/QMA rfa/v 0,4 r4 o b ,RECORD MED/UM AFTER RECORD/NG 0 C IN VENTOR.

United States Patent O.F

The inventionrelates in general to magnetic recording of information data by means of athermal transducer and more particularly torecording by demagnetizing por- Y tions of a fully magnetized record medium by means of a Peltier effect thermoelectric junction.

It `has hitherto been known that if Vtwo dissimilar mav terials are joined in electrical contact in such a way as to form two junctions and an electric current is forced ,to flow in the circuit, one of the junctions absorbs heat and the other junction liberates heat. If the current is reversed the first junction liberates heat instead of absorbing heat and the second junction absorbs heat. It has also hitherto been known thatcertain materials can be magnetized by being placed for a short period of time in a magnetic field and those premagnetized materials can be caused to become randomly magnetized or, as commonly called, demagnetized by heating above a certain temperature, known as its Curie temperature or Curie point'.

The present invention contemplates using a thermo electric Peltier junction in contact with a translated pre- -magnetized record surf-ace, and applying to the junction an electromotive force corresponding to the signal sought to be recorded in order to heat the junction to selectively demagnetize portions of they record surface and to cool the junction so as to leave other portions of the record surface unaltered. By translating the record surface at a predetermined velocity and by precise timing of the signal, a magnetic recording of the information data can thus be obtained, such recording being capable of being read by any electromagnetic transducer well known in the art.

The invention is of particular importance in relation to recording of bits of information data as are employed in dynamic magnetic storage devices of the tape, disc, drum, and the like, types.

One object of the invention is therefore to provide a method and means for recording information on a premagnetized medium by demagnetizing portions thereof by selective and timed localized heating above the Curie point of the materials forming the premagnetized medium.

Another object of the invention is to provide athermal transducer capable of electing such a recording.

A further object of the invention is to provide a thermal transducer with a low thermal inertia'thereby allowing it to heat rapidly when an electric current is flowing in one direction and to cool rapidly when an electric current is flowing in the opposite direction.

Another object of the invention is to provide a thermal transducer which can be manufactured cheaply and which may operate for long periods of time without deterioration.

Otherobjects and advantages will become apparent from the following description taken in connection with the accompanying drawings, wherein:

FIGURE 1 is a schematic diagram of an apparatus y 3 ,187,335 Patented June 1, 1965l "ice URE l, comprises a thermal transducer cooperating with a record support having a recording surface thereon consisting of a magnetizable material such as, for example, manganese-arsenic, chromium-telluriurn or manganesebismuth, having respectively Curie points of 45 C., 100 C. and 350 C.l

The recording surface is premagnetized land is displaced in contact with the thermal transistor consisting of two rods of similar semiconductor materials such as, for example, bismuth telluride- (BizTea), lead telluride (PbTe),` bismuth selenide (Bi2Se3), antimony Vtelluride (Sb2'l`e3), or the like. One rod is a P-type doped with acceptor impurities such as lead, zinc, aluminum, gallium, etc., and the other rod is an N-type doped with donor impurities such as iodine, tellurium, arsenic, phosphorus, etc, The rods taper to a point forming ajunction, identied .as a primary Peltier junction in the drawing, and the free ends of the rods form two other junctions with the conductors connected thereon, identified as secondary Peltier junctions. The latter junctions act as cold junctions wheny the primary Peltier junction becomes hot vand as hot junctions when the primary Peltier junction becomes cold. The conductors are of metal such as copper, silver or aluminum and have terminals acrossrwhich an input signal in the form of a succession of electrical pulses may be applied.

cells 1 to 8, for thel sake of explanation.

constructed in accordance with the teaching of `the invention', and

FIGURE 2 is a diagrammatica-l graphical representation of Wave forms plotted to a common time scale and helpful in understanding the basic principle of the invention.

The invention, as schematically represented in vFIG- When the electric current flows in one direction heat is generated at the primary Peltier junction in contact with the recording surface and heat is transmitted to the recording surface destroying the magnetism of the surface at the point of contact. When current iiows in the opposite direction the primary Peltier junction is almostinstantaneously cooled and the magnetized state of the recording surface is left undisturbed. By relative timed translation between the recording surface and the primary Peltier junction, a succession of unmagnetized and magnetized spots are left upon the recording surface as long as the spots sought to be demagnetized are heated above the Curie point of the materials of the recording surface, and as long as the junction is rapidly cooled to a temperature below the Curie point to leave undisturbed the spots sought to be left magnetized.

It has been experimentally found that the spots heated above the Curie point may actually be left in a magnetic state in a direction opposite to the magnetic state of the non-heated portions of the recording surface; in other words, if the recording surface has been pre-biased to a positive saturation level, for example, the heated spots tend to present a negative level rather than a zero level.

Referring now to FIGURE 2, timed bit cells on the path of the thermal transducer are arbitrarily identified as bit FIGURE 2(a) represents a constant magnetization level B of the recording surface previously to recording of information.

FIGURE 2(b) illustrates graphically a representation of binary number l0ll0010 (number 178 indecimal notation) which could be recorded byrecording a one in bit cell 1, a zero in bit cell 2, a one in bit cells 3 and 4, a zero in bit cells 5 and 6, a one in bit cell 7 and a Zero in bit cell 8.

FIGUREY 2(c) is an idealized representation of the state of the record medium after the signal of FIGURE 2(b) has been applied across the input of the thermal transducer in such a way as to cause-the junction to become hot for every negative pulse representing a zero and to cool by reversalof current for every positive pulse representing a one, causing in turn the recording surface to be respectively heated above its Curie point or maintained at a temperature below its Curie -point'as explained hereinbefore. It is evident that in actual practice the pulses recorded on the recording surface are not as 3 Y j sharp as graphically represented on the diagram of FIG- URE 2(6) and that the zero bits may actually become negative as also explained hereinbefore.

1It is obvious that the principleof the invention is applicable to any method of magnetic information recording such as.return to bias, non-return to zero, phase modulation, and the like, and it`will be apparent toA those skilled in the art that the compositions of materials herein given for both. the thermal transducer and the recording surface, together lwith the physical representation of the invention in the drawings, are for illustrative purpose only, and that many other embodiments are within the scope an'dspiritj of therinvjention as defined in the appended claims. I.

What is claimed as new is: l. .In combination: a record medium having a magnetizable surfacethereon which has been premagnetized to a predetermined level; a thermal transducer in contact with said surface, said transducer comprising a P-N junetion of semiconductor material capable ofY beingheated and cooled accordinglto the direction of an electrical cur- -rent owing therethrough; and means for translating said surface in timed relationship relatively to said transducer;

-whereb'y when said transducer is heated above the Curie pointof the material of said surface, portions of said 'surface are:selectively demagnetized in the path of said pulse. i 1 .,3. In. combination: a thermoelectric Peltier junction capable of becoming heated during the period of time that an elcctromotive force is applied to said junction to cause a current to llow thereacross in one direction and capable of being cooled as soon as the current reverses itself, said junction tapering to a narrow gap; a record medium having a magnetic surface thereon which has been premagnetized to a predetermined level, said record medium being translated in relation to said junction in contact with said gap; lwhereby some portions of said surface are lselectivelydemagnetized by heating above the Curie point of the materials of.` said surface, and the remaining of saidsurface is left substantially undisturbed.

4. The apparatus of claim 3 wherein the thermoelectric junction isaV P-N junction of semiconductor materials. i 5. Theapparatus of claim wherein the eletrornotive vforce applied across the thermoelectric junction is in the shape of alternating directcurrent pulses of vtimed d urations. r y

6.Magnetic recording comprising: V,Peltier junction :meansv eapableof being alternately heated and cooled according` to thedirection of an electric current command signal ,through said ,meanspmeans translated in contact with said rst mentioned means, s aid second mentioned means comprising premagnetized' lmaterialsV capable ofbeing selectivelydemagnetized when heated above a-predetermined temperature by s aid rst mentioned means.

7. Magnetic recording according to claim 6 wherein the electric current command signal is an electrical pulse of timed duration.

References Cited bythe Examiner UNITED "STATES PATENTS.l

l 2,915,594 1/59 VBurns et al. 1797-1002 2,979,572 4/ 62 Levin 179-1002 3,072,751 1/63 Zworykin et al. 179-1002 f 13,094,699. 6/63 Snpernowicz 179-1002 rRvING L, sRAGoW, Primary Examiner. 

3. IN COMBINATION: A THERMOELECTRIC PELTIER JUNCTION CAPABLE OF BECOMING HEATED DURING THE PERIOD OF TIME THAT AN ELECTROMOTIVE FORCE IS APPLIED TO SAID JUNCTION TO CAUSE A CURRENT TO FLOW THEREACROSS IN ONE DIRECTION AND CAPABLE OF BEING COOLED AS SOON AS THE CURRENT REVERSES ITSELF, SAID JUNCTION TAPERING TO A NARROW GAP; A RECORD MEDIUM HAVING A MAGNETIC SURFACE THEREON WHICH HAS BEEN PREMAGNETIZED TO A PREDETERMINED LEVEL, SAID RECORD MEDIUM BEING TRANSLATED IN RELATION TO SAID JUNCTION IN CONTACT WITH SAID GAP; WHEREBY SOME PORTIONS OF SAID SURFACE ARE SELECTIVELY DEMAGNETIZED BY HEATING ABOVE THE 